A REVIEW OF NITROGEN INFLATION....
                                                       OF PNEUMATIC TIRES
By: Harold J Herzlich

This REVIEW will focus in on accepted scientific principles and peer reviewed scientific papers that form the basis for an expected nitrogen tire inflation customary and usual practices paradigm shift.

In a recently published article in Tire Business, Herzlich stated the following: "Nitrogen’s slower permeability characteristics coupled with its bone-dry nature may partially ameliorate some field abuse conditions, including long term inflation maintenance neglect, improper repairs and certain types of tire pressure monitor malfunctions. Even though high purity nitrogen is no guarantee of performance and will not undo the many forms of damage or abuse that can lead to tire failure, it offers a low cost, risk free and positive service opportunity that has finally become commercially and technically practical". Based upon published long term oxidation tire weakening theories accepted by the scientific community, the required 95%+ level of nitrogen purity in the tire should be a primary consideration if the long term benefit of this technology is to be fully realized.

A 1970 paper by L Sperberg, "Tire Durability With Nitrogen Inflation" documented various durability and service advantages for this method. The subject with regard to the general motoring public remained dormant since a reliable, cost effective and safe nitrogen source was not available.

In 1998 Bridgestone, Firestone took a positive nitrogen inflation position: (Technical Bulletin P-047-X). stating that "nitrogen is acceptable as an inflation gas for use in Bridgestone and Firestone passenger, light truck and truck tires."

In 2000, a well known independent consultant to truck fleets, Peggy Fisher issued the statement that "Air May Be Out For Tire Inflation" and reinforced all opinions regarding the benefits of nitrogen tire inflation www.truckstoptravelplaza.com/2000/n1/tirewheel.html

In 2003 Bridgestone took a stronger proactive position advocating dry, high purity nitrogen inflation (Should You Stop Putting Air In Your Tires, Vol 8, Issue 3, www.trucktires.com).

Cited advantages were:
1. Less inflation Loss ("six months to lose 2 psi with nitrogen compared to just a month with air")
2. Less Inflation Pressure Fluctuation ("tires inflated with wet air tend to run hotter and fluctuate in pressure more")
3. Reduced Wheel Corrosion ("oxygen corrodes aluminum and steel wheels... .rust can clog valve stems, causing them to leak")
4. Safety ("nitrogen is used in off-highway and aircraft tires ...which can run so hot they can actually catch on fire").

Michelin, BF Goodrich, Uniroyal, Riken, Cavalier issued a joint Technical Bulletin in November, 2003 which stated that, "Michelin supports the use of nitrogen on its ability to better retain air over a period of time".

Goodyear, in a June 14, 2004 Product Service Bulletin #2004-09 stated, "Goodyear supports the use of nitrogen, as an inflation gas, in all Goodyear, Dunlop, Kelly, and Associate Brand and Private Brand products, based on the ability for the tire to retain pressure for a longer period of time. The use of nitrogen will not affect the tire warranty".

In 2005, The Retread Information Bureau issued a news release, "Why Inflating Tires With Nitrogen Makes Sense" and included the statement, "By extending the useful life of a tire, retreading offers additional environmental benefits."

In Europe, there have been additional activities supporting the nitrogen inflation concept. Air Liquide in France claimed a... "25% improvement in tire life since tires stay inflated longer because nitrogen migrates 3 times slower than air and nitrogen eliminates internal oxidation of the tire so more retreads can be achieved." Liquide claimed... 30% savings on tires and fuel.

While aircraft tires have a unique set of needs that include pressure retention, non-explosive inflation gas, no moisture and excellent recappability, their required use of the inert high purity nitrogen validates its’ desirability in all pneumatic tires.

Numerous articles since the 70's have shown advantages for nitrogen inflation and its’ beneficial effect on the retention of the tire components’ original properties.

In a September 20, 2004 technical article in the largest international rubber industry trade paper, Rubber and Plastics News, Dr. J Baldwin of Ford presented his peer reviewed findings "Passenger Tires Inflated With Nitrogen Age Slower". Some of his conclusions included, "lower permeability than oxygen (better gas mileage), more controlled inflation pressure due to the absence of moisture, expected improvement in structural durability due to significant reduction in rubber oxidation (oxidation caused by air from the cavity being forced into the tire carcass".

Herzlich, a tire industry consulting Chemical Engineer with 50 years industry experience stated in a Tire Business Article October 24, 2005 that "Nitrogen’s slower permeability characteristics coupled with its bone-dry nature may partially ameliorate some field abuse conditions, including long term inflation maintenance neglect, improper repairs and certain types of tire pressure monitor malfunctions. Even though high purity nitrogen is no guarantee of performance and will not undo the many forms of damage or abuse that can lead to tire failure, it offers a low cost, risk free and positive service opportunity that has finally become commercially and technically practical".

As already noted, nitrogen inflation of tires is not new. For many years very high pressure bottled high purity nitrogen was the only source used to inflate tires having critical service requirements (i.e.: aircraft, giant earthmover and race cars).

The real world of tire durability and fuel economy performance is complex and includes a large population of tires that have been exposed to a wide range of damaging service conditions that cause excessive deflection (distortion and heat generation) which accelerates oxidative and thermal degradation. Nitrogen inflation will not undo many forms of tire damage that lead to failure.

Both oxidation and thermal weakening (not aging) of the tire structure are scientifically accepted mechanisms that can contribute to some common types of tire failures. Under inflation, which is a major contributor to the oxidation/thermal degradation process, also results in reduced tread life and increased fuel consumption. Under inflation results in the higher rolling resistance that pollutes the air as it unnecessarily burns hundreds of millions of gallons of fuel each year. Under inflation creates other safety issues such a marginal and unpredictable vehicle controllability.

High purity nitrogen inflation, by partially addressing some of these issues and concerns, may bring about an important paradigm shift in tire maintenance practices. As its’ value is communicated and accepted by the public and regulatory officials, high purity nitrogen inflation can become the state of the art practice for tire service operations.


ECONOMIC ADVANTAGES FOR HIGH PURITY NITROGEN INFLATION

Air is composed of about 78.1% nitrogen and about 20.9% oxygen. Air also can contain significant and variable levels of water vapor and contaminants from the compressor system. Since oxygen diffuses through rubber at about 3 times the rate of nitrogen, a tire will retain its pressure longer when inflated with high purity nitrogen. Herzlich showed that 96% nitrogen tires stored for 30 days at a range of elevated temperatures lost 2.2% less pressure than similar tires inflated with air. While this appears to be a small difference, one must consider this effect over a much longer period of time and with different tire sizing configurations and with tens of millions of tires.

The effect of tire inflation pressure on fuel economy is apparent to any person riding a bicycle with under inflated tires. A range of peer reviewed tire industry papers confirm that under inflation is a serious and common reality that diminishes auto safety for a variety of reasons. T Laclair, Michelin, Tire Science and Technology, "Truck Tire Operating Temperatures on Flat and Curved Test Surfaces" Vol 33, No. 3. Laclair states that "operating temperature is critical to the endurance life of a tire". Under inflation is a critical heat contributing tire performance deficit.

Oxidation of rubber follows the basic laws of chemistry. The rate of chemical oxidation is highly dependent upon temperature and roughly doubles for every 18 degrees increase in the tires operating temperature. Under inflation raises the operating temperature of the tire; thereby increasing the rate of its oxidative weakening. Higher ambient temperatures (ie: Southwest) add significantly to the thermal stress created by under inflation.

BF Goodrich scientists documented additional inflation information in a paper by Beatty and Miksch,"Some Effects of Tire Inflation On Radial Tire Performance", Rubber Division, ACS, Las Vegas, NV, Paper 45, May 22, 1980

Weeks and Sheets, Effects of Tire Pressure and Performance Upon Oil Use and Energy Policy Options", Proceedings of the Intersociety Energy Conservation Engineering Conference, 1991, estimated that a tire with 28% under inflation (25 psi instead of 35 psi) would consume about 3.8% more fuel over a 100,000 mile service life span of the vehicle. They based this upon data that showed a force resisting the rolling of the tire to be about 18 pounds for a 35 psi tire vs. 26 pounds rolling resistance for the same tire at 25 psi inflation. This would calculate out to about $70 per year per vehicle of increased fuel cost. When one adds the shorter tread life for the over deflected tire, one can easily estimate a significant added cost coupled with reduced reliability when running moderately under inflated tires.

Tracey and Waddell of Exxon in their published 2004 International Tire Exhibition and Conference paper, "Halobutyl Innerliners Offer Best Tire Durability", reported that a 20% deficiency in tire inflation pressure reduced durability by 20%.

Coddington of Exxon in his paper, Tire Inflation Pressure Loss, Its Causes and Effects, 5th Australasian Rubber Technology Conference, quantified under inflation deficiency stages. He also demonstrated the temperature variability of pressure loss and the greater tendency for small tires to be more severely affected. The mini-spare high pressure tire is very vulnerable to this high surface to low volume permeation effect.

Volvo Cars Nederland RV in a press release "Nitrogen in Auto Tires Helps the Environment and Safety. Volvo Prefers Nitrogen in Auto Tires (Volvo Prefereert Stiksof in Autobanden)" Volvo stated that "scientific research has proven that the use of nitrogen as inflation gas for auto tires gives many advantages compared to normal compressed air. A tire with 20% under inflation uses 2 to 3% more fuel than a tire with the proper pressure. Volvo Cars Netherlands expects that the Volvo dealers will follow and implement this environmentally beneficial initiative ... every tire is eligible to be filled with nitrogen." Volvo is a division of Ford Motor Company.

Based roughly upon about 206 million passenger cars and light trucks in operation (and estimating 25 gallons saved annually by each vehicle) proper inflation would reduce annual gasoline consumption by about 5 billion gallons and eliminate the air pollution created by 15 million tons of unnecessary gasoline combustion.

The increased muscle energy required to move the bicycle with soft tires is an example of the increased fuel needed to move a vehicle with "soft" tires. While the power of the engine masks the negative effect on rolling resistance, the simple observation of the vehicles increased pep after an oil change is usually mistakenly attributed to the "clean oil" that was just put into the engine. Actually it is more likely due to the tires being aired up during the express oil change service.

The presence of moisture in the inflation air of tires causes deviations in the way the inflation pressure changes as the tire operates. Dry high purity nitrogen eliminates moisture caused deviations in tire pressure. Moisture and oil in the compressed air system makes the valve core and/or the pressure monitoring device less reliable. Allegations of expensive damage or critical malfunction to the pressure monitoring device will be a matter of increasing responsibility to people servicing tires. Dry nitrogen will reduce the validity of certain claims.


CHEMICAL FACTORS JUSTIFYING HIGH PURITY NITROGEN INFLATION

Oxygen, while necessary for life, is in reality an aggressively corrosive gas that attacks the rubber molecule and other critical chemicals in the tire as it dissolves and diffuses through the structure. Depending upon the nature of the rubber molecule, the oxidative process irreversibly weakens the tire Hunter, Datta and Noordermeer from the Netherlands in their Rubber Chemistry and Technology Literature Review Article of 2004, Vol 77, No. 3, Pg 476 " Addressing Durability of Rubber Compounds" identified the accepted oxidation chain reaction responsible for weakening process. The literature also describes the diminishing effects of antioxidant additives over longer periods.

The detrimental effect of oxygen on the fatigue and fracture properties of rubber has been demonstrated by studies that show faster rates of crack growth, shorter fatigue life and greater susceptibility to severe strains.

While tire "aging" has become a topic of interest with regard to long term tire reliability and durability, the chronological age of a tire by itself has little bearing on the tires weakening process that is associated with actual failures. The weakening of general purpose rubber such as used in tires is an oxidation/service condition process. Abusive service conditions such as under inflation or overloading accelerate the degradation process.

Uniroyal paper 18D17 "Long Term Durability of Tires by N Tokita" established that "one reason for loss of long term durability is oxidative reactions in the breaker stock during service ... the tear strength of the breaker stock excised from the oxygen aged tires for unaged, accelerated aged and accelerated aged showed rubber deterioration, whereas the tire filled with pure nitrogen showed little.. ....From these laboratory tests, we conclude that the oxidative changes of the breaker stock is a inevitable cause of the limited service life." This paper finds that the decrease in the relative rubber strength relates to an increase in oxygen absorbed.

A Goodyear Tire and Rubber Company paper presented at the International Tire Exhibition and Conference (2004) by Dr. M Cohen, "How Tires Age and How To Characterize Aging In Tires" demonstrated a steady increase in oxygen content at the belt-edge from sets of consumer tires that were in service for longer service periods. The effect of oxygen content on the reduction of laboratory fatigue life was significant as the oxygen content increased. Laboratory studies showed "faster crack growth in air (100 kilocycles) than in a nitrogen atmosphere (450 kilocycles). Data also demonstrated that higher inflation pressure accelerated the rate of oxygen take-up. This will become more important as tire pressure specifications will increase for improved fuel economy (now as high as 51 psi (350 kPa) in some passenger tires.)

Baldwin, J M, (Baldwin, JM, Bauer, DR, Ellwood, KE, Passenger Tires Inflated With Nitrogen Age Slower, Rubber and Plastics News, September 20, 2004) clearly established that passenger tires inflated with nitrogen age slower. In his work, "tires inflated with 96 percent and 99.9 percent nitrogen were oven aged at 60C (140F) for three to twelve weeks. For comparison, tires inflated with either air (80%/20% or 50%/50%) nitrogen/oxygen were oven aged alongside the nitrogen inflated tires". "The tires inflated with more than 95 percent nitrogen do not appear to change very much from the new tires even after 12 weeks in the oven, whereas the tires inflated with the oxygenated media change dramatically, even after three weeks in the oven."  Further analysis validated Baldwin’s conclusions that, "...tires inflated with more than 95 percent nitrogen do not appear to change very much from new tires." After twelve weeks of this very aggressive laboratory aging condition, Baldwin concluded that, at 12 weeks tires inflated with 96 percent nitrogen......the beginning of oxidative degradation can be seen. Nitrogen inflated tires, however degrade far slower than tires inflated with the oxygenated media.

It is based upon this 96 percent nitrogen finding that it is not recommended to exceed 4 or 5 percent oxygen in the tire.

Other Baldwin conclusions were "the oxidation of the steel belt rubber is truly driven from the contained air pressure .... the skim may be oxidized slightly from the outside when nitrogen filled, but the rate of degradation is significantly lower than when the tire is filled with air" Baldwin demonstrated that the peel strength changes in the 95 percent nitrogen exposed samples progressed at a much slower rate than the samples exposed to air. The fact that he was still able to see very slow oxidation in the 95 percent nitrogen exposed samples amplifies the expectation of a loss of the nitrogen durability benefits as one goes to lower levels of purity.

Baldwin states: "The overall conclusion of the study is: When nitrogen is used as the inflation media, the change in rubber properties is significantly slowed down or even halted."

Based upon the above findings gas purity level monitoring of the nitrogen generation process is an important part of the nitrogen inflation process.


TIRE TEST RESULTS NHTSA

The Department of Transportation DOT  has under review tire manufacturers recommendations of an endurance wheel test using 50% oxygen enriched inflation gas to accelerate the long term oxidation weakening of tires. This in itself adds weight to the potential value of inert pure nitrogen gas inflation.

Coddington showed a significant improvement in oxidation resistance and tire durability when a nitrogen gas was used in place of air. In his "Factors in Tubeless Radial Tire Durability" June 1993, he described work by N Tokita which found that "oxygen aged tires showed a major reduction of strength while those inflated with nitrogen showed slight loss.

Test data that was reported under varied aging conditions showed:

Aging Conditions                                                          Relative Strength, %
       Un-aged                                                                           100
    O2 20cycles                                                                     34 - 38
    N2 20 cycles                                                                    84 - 90
N2 aged 110hrs/115C                                                              80


Coddington also reported tire data:

Variable                                                                Wheel Test Hours To Failure
Air inflated                                                               215 hours, 240 hours
Nitrogen inflated                                                       no failure, 600 hours

Listed below are probable real world advantages for high purity nitrogen inflation.

Innerliner violations such as improper repairs, punctures, impact damage and bead mounting damage take place in tires and the resulting intra carcass oxidative pressurization is an accepted causation of tire tread detachments. Regardless of how effective the inner liner is, it cannot perform when it is violated by service misuse.

Nitrogen, which is bone dry, will also eliminate moisture moving into the casing and attacking the fabric/ steel reinforcement/ adhesion systems as well as attacking the wheel/valve/pressure monitoring system.

Run flat tire configurations, which generate higher temperatures while running disabled, will benefit from a less combustible mix in the violated air chamber. Medium over the road truck tires with duals are sometimes subject to very high temperature overload/under inflation running conditions that can initiate internal combustion within the air chamber. Pure nitrogen inflation will reduce this combustion possibility.

Truck casings will be in a more recappable, higher value condition because of their reduced oxidation and under inflation history.

Nitrogen inflation will contribute to the long term storage and durability of an inflated spare tire which requires optimum pressure retention and static inflated aging/high temperature storage oxidation resistance.

High purity nitrogen inflation concept will encourage the motorist to be more aware of specialized high quality tire maintenance. This can be raised to the same attention level as an oil change schedule. This will also encourage return visits the dealer (non generic, high quality nitrogen source) giving opportunity for inspection and ROTATION.

CURRICULUM VITAE

HAROLD J HERZLICH, BChE
HERZLICH CONSULTING, INC.
TIRE ENGINEERING AND CHEMISTRY

EDUCATION
New York University, University Heights, Pre-Medical, College of Engineering, Chemical Engineering - ’56
Southern Connecticut College - Graduate Chemistry Program, Polymer Chemistry, ASM - Corrosion
University of Wisconsin - Instructions and Warnings
Nevada Community College - Philosophy of Critical Thinking
Quinnipiac College - Graduate Business Program, Marketing Economics, Export Marketing, Statistical Decision Making, Private Investigator Skills and Techniques, Private Security Rules & Regulations, Private Security Investigator, Ethics
Alexander Hamilton Business

Miscellaneous - Tire Engineering, Rubber Chemistry, Management, Quality College, Tire Mechanics and Vehicle Handling, Vehicle Rollover Mechanics, Aerospace Landing Gear Systems, Sudden Air out , Wet Skid , Ice/Snow Traction, Tread Detachment , Mismounting Bead Rupture, Over Deflection Hysteresis, SEMA 93-04

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